The invention relates to a mount having hydraulic damping action and, more particularly, a mount for mounting an engine on the chassis of a vehicle and a membrane therefor.
A known mount has a pedestal and a mounting bracket with an annular spring element therebetween. These enclose variable-volume working and equalizing spaces. The working and equalizing spaces are filled with an hydraulic fluid and communicate through a throttle opening for hydraulically damping relative movement of the pedestal and mounting bracket which varies the volume of the working space to produce a pressure differential between the spaces for hydraulic fluid flow through the throttle opening therebetween. A membrane separates the working and equalizing spaces by securing the periphery of the membrane to the mounting bracket. The pressure differential between the working and equalizing spaces thus bulges the membrane in the direction of the working or equalizing space having the lower pressure. A portion of the membrane is cut through nonrectilinearly to open to form a pressure-relief channel between the working and equalizing spaces, in addition to the throttle opening, when a sufficient pressure differential bulges the membrane sufficiently.
An engine mount of this type is described in published German patent application No. 32 25 701. Its membrane is disposed between symmetrically-positioned grid plates which are rigidly attached to the mounting bracket and bear with some initial tension on either side of the membrane. Its nonrectilinear, membrane cuts intersect the openings in the grid plates, the nonlinearity of the cuts being very slight. It damps well moderately-large-amplitude, low-frequency (below about 30 Hz) vibrations produced, for example, as a vehicle with the engine mount travels over rough ground. It has, however, the drawbacks in operation of being inherently noisy and undesirably transmitting to the chassis of the vehicle both high-frequency (over about 30 Hz) vibrations and larger-amplitude, low-frequency (below about 30 Hz) shaking produced, for example, when the engine is turned on and off. Vibrations and shaking of this kind are not well isolated.
Damping and isolating vibrations usually require measures which functionally interfere with each other. As usual, this is the case with the engine mount referred to above. The damping action, desirable for the vibrations of traveling over rough ground, is obtained at the expense of good isolating action, desirable for the shaking motion which occurs when turning the engine on and off. The engine mount referred to above thus represents merely a more or less unsatisfactory compromise.
U.K. Pat. No. 811,748 describes a similar mount design. Its membrane between the working and equalizing spaces has a calibrated opening instead of a cut. The membrane is clamped in proximity to its outer periphery between flanges which are rigidly united with the mounting bracket. The mount is, nevertheless, afflicted with the same drawbacks as the one mentioned earlier.